In recent years, as information recording has been raised in density and digitized, the developments of various information recording/reproducing systems have been carried forward. In particular, optical discs which utilize the light energies of lasers for recording, erasing and reproducing information are capable of higher recording densities as compared with magnetic discs, and they are promising systems for future information recording. Among them, the reproducing device utilizing the laser has been put into practical use as a compact disc (CD). On the other hand, the systems capable of recording are broadly classified into two types; the add-on type and the rewritable type. The former can write information only once and cannot erase it. The latter is a system capable of repeated writing and erasing. The recording method of the add-on type is such that the recording part of a medium is destroyed or molded into a rugged part by laser light, and the reproduction makes use of the change of the amount of light reflection based on the interference of laser light at the rugged part. It is generally known that Te or an alloy thereof is utilized for the recording medium so as to form the rugged part through the fusion or sublimation of the material. The medium of this sort involves some problems such as toxicity. As the recording media of the rewritable type, optomagnetic materials form the mainstream. With this method, information is recorded in such a way that the local magnetic anisotropy of the medium is inverted at or near the temperature of the Curie point or compensation point thereof by utilizing light energy, and it is reproduced owing to the magnitude of rotation of a polarization plane based on the magnetic Faraday effect and magnetic Kerr effect of polarization input light at the corresponding part. As the most promising method for rewritability, this method is being energetically studied and developed with the aim at practical use several years hence. Another system of the rewritable type exploits the change of a reflection rate based on the reversible phase change between the amorphous state and the crystalline state of a recording medium. An example of the recording medium is made of an amorphous - crystalline phase transformation type material in which TeO.sub.x is doped with small amounts of Ge and Sn as described in `National Technical Report`, Vol. 29, No. 5 (1983).
With this system, however, the crystallization temperature of the amorphous phase is low, so that the phase of the material is unstable at the normal temperature.
Meanwhile, a method wherein a recorded content is erased by causing direct current to flow through a recording medium is disclosed in, for example, Japanese Patent Application Laid-open No. 59-79436 entitled `Information recording, reproducing and erasing method` laid open on May 8, 1984. This method consists in that direct current is caused to flow through an electrochromic material such as WO.sub.3 in contact therewith, whereby a recorded content is erased. It has the disadvantage that a recorded content disappears naturally with the lapse of time.